I have re-installed KaOS, using the same USB stick as yesterday. This time I opted to have swap enabled.
After the install, lock screen worked OK, as did the energy settings.
But: once I connected to the internet, octopi informed me that 107 packages needed updating (after my previous installation yesterday, this updated happened together with the installation of Firefox en Chrome).
After the update, the lock screen has lost the fields needed to unlock the screen. Hence in this update is something that changed the lock screen and makes unlocking impossible. Pacman.log: https://pastebin.com/FQM6ndQc.
Energy saving continues to work - hence my conclusion that switching off the screen one way or another needs swap space (I do not see why but this is the only difference between my installation yesterday en my installation today)